In a large prospective cohort, nighttime values were especially good at predicting cardiovascular and renal events, according to Roberto Minutolo, MD, PhD, of the Second University of Naples in Italy, and colleagues.

But measuring blood pressure in the doctor's office had no predictive value, Minutolo and colleagues reported in the June issue of Archives of Internal Medicine.

The effect was seen even after researchers excluded 189 patients -- of a total of 436 – who had so-called "white coat hypertension," usually defined as elevated blood pressure in a clinical setting.

But the guidelines have recently become controversial, they noted, and it may be that in some patients (the elderly or those with white coat hypertension), efforts to control blood pressure may actually be dangerous.

To help clarify the issue, Minutolo and colleagues looked at the prognostic role of daytime and nighttime systolic and diastolic blood pressure in comparison with office measurements.

Consecutive patients in four Italian centers had blood pressure measured during an office visit, at which the ambulatory measurement device was fitted. A second office measurement was made the following day, after 24 hours of ambulatory measurements.

The primary end points of the analysis were time to end-stage renal disease or death and time to fatal and nonfatal cardiovascular events, the researchers said.

During a median follow-up of 4.2 years, 155 and 103 patients, respectively, reached those endpoints, they reported.

Analysis showed:

Office blood pressure measurements did not predict either outcome.

Compared with a daytime systolic pressure of 126 to 135 mm Hg, those whose pressure was 136 to 146 mm Hg, or greater than 146 mm Hg, had an increased cardiovascular risk. The hazard ratios were 2.23 and 3.07, respectively, with 95% confidence intervals from 1.13 to 4.41 and from 1.54 to 6.09.

The same was true for the renal endpoint, with hazard ratios of 1.72 and 1.85, respectively, with 95% confidence intervals from 1.02 to 2.89 and from 1.11 to 3.08.

Nighttime systolic pressures of 125 to 137, or higher than 137 mm Hg, also increased the cardiovascular risk significantly, with hazard ratios of 2.52 and 4.00, respectively, compared with the reference value of 106 to 114 mm Hg.

Those elevated nighttime systolic pressures also significantly increased the renal risk, with hazard ratios of 1.87 and 2.54, respectively.

Similar patterns were seen for diastolic pressure.

The findings suggest that interventional studies, based on ambulatory measurements, are "urgently required in this high-risk population," Minutolo and colleagues concluded.

The researchers cautioned that the study had only a few diabetic patients and was racially homogenous, and therefore might not apply directly to more diverse populations. As well, they added, the ambulatory blood pressure data were based on a single set of measurements, which might have lead to some imprecision.

They also noted that about 90% of patients were on antihypertensive medication, while those with normal blood pressure in the absence of medications were excluded.

The study is "both exciting and challenging," according to David Goldsmith, FRCP, of Guy's Hospital in London, and Adrian Covic, MD, PhD, FRCP (Lond), of C.I. Parhon University Hospital in Iasi, Romania.

On one hand, they argued in an accompanying invited comment, "there will be those who will question the time, effort, and expense of running an ambulatory [blood pressure] service."

On the other hand, the study makes the case for such a service stronger, at least in a selected cohort of patients, they argued. If nephrologists are serious about targeting blood pressure, they wrote, "it is now harder to defend reliance on clinic (blood pressure) measurement alone."

What's needed now is a randomized trial to investigate the issue, Goldsmith and Covic concluded.

The authors did not report any external support for the study. They made no financial disclosures.

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